Polymer scale which builds up on the walls of reactors during polymerization causes a problem for polymer manufacturers. Polymer scale deposited on the various surfaces within the polymerization reactor causes a decrease in polymer yield and a reduction in the cooling capacity of the polymerization reactor. Further, the polymer scale deposited on the surfaces tends to come off and enters into the polymer product, resulting in production of a polymer product of lower quality. Furthermore, the removal of scale from the inner surfaces after each polymerization run requires large amounts of labor and time, resulting in the reduction of productivity. Additionally, inhalation of volatile monomers, especially vinyl chloride during the scale-removing operation causes serious health problems.
To solve such problems, a number of methods have been proposed to prevent polymer scale deposition, specifically in the suspension polymerization of vinyl chloride or a monomer mixture composed mainly of vinyl chloride. In some methods ingredients are added during the polymerization reaction itself. In other methods the walls of the reactor are sprayed with an inert film containing scale preventing agents, such as dyes or condensation polymer, most of which are prepared by other procedures. These prior art methods have, in fact, been successful in some cases for the commercial production of polyvinylchloride (PVC) resin. But certain disadvantages still exist.
Spraying an inert film on the inner walls of a polymerization reactor to prevent polymer scale buildup has a fatal defect in that it is impossible to spray coat homogeneously. Additionally, spraying to every point of the reactor still leaves many pinholes on surfaces of the reactor after the solvent evaporates and allows unreacted monomers to come in contact with the inner surfaces of the reactors and cause corrosion. Therefore, there is a need to overcome these defects in the spray coating methods of preventing scale.
The present invention is an electrochemical method. The well-known compound, phenol and its alkyl derivatives are weak acids with pK values of about 10 (in water). The electrochemical oxidation of these phenol compounds produces products of high molecular weight, especially where the procedure is carried out in a non-aqueous system. In the present invention wherein the polymerization reactor acts as the anode and an iron bar as the cathode, phenol and its halo and alkyl derivatives are electrolyzed using a non-aqueous solvent and a Lewis Base. A thin organic coating is produced which adheres to the reactor's inner walls. This coating prevents the deposit of scale on the wall. The coating being substantially pinhole-free also prevents pass through of monomers to the inner surfaces of the reactor during polymerization.